N, P Co-doped porous biochar derived from cornstalk for high performance CO2 adsorption and electrochemical energy storage

Modification of biomass-derived porous biochar by heteroatomic doping can significantly improve CO2 adsorption and capacitance performance of supercapacitors. In this study, a novel N, P co-doped porous biochar was developed by facile two-step pyrolysis using widely available and low-cost cornstalks as the carbon source, melamine as the N source, phytic acid as the P source, and a mild K2CO3 as an activating agent. The pore structures and surface chemical characteristics of the as-prepared N, P co-doped cornstalk-derived porous biochar (abbreviated as NPCPB) were regulated by adjusting the pyrolysis temperature and K2CO3 ratio. The as-prepared NPCPB-600-3 (600 represents an activation temperature of 600 °C, and 3 represents the mass ratio of K2CO3 to the carbon composite precursor is 3) was characterized by various methods, and its CO2 adsorption and electrochemical properties were studied. Results indicated that narrow micropores and N, P doping together determined the adsorption capacity, which was 3.11 mmol g−1 for CO2 at 1 bar and 25 °C, with almost no decay after 10 consecutive cycles. NPCPB-600-2 had a superior specific capacity of 203.5 F g−1 at a current density of 1 A g−1 and an outstanding cycling stability with a good capacity retention of 106% after 5000 cycles at a high current density of 10 A g−1. This work reveals that heteroatomically doped porous biochar from biomass has a promising application in CO2 capture and supercapacitors.